Silicon nitride is commonly utilized as an insulative material during semiconductor device fabrication. For instance, silicon nitride can be utilized as a dielectric material in capacitor constructions. Another use for silicon nitride in semiconductor device fabrication is as a barrier layer to impede migration of, for example, oxygen, hydrogen, and metallic materials.
It can be desired to simultaneously deposit silicon nitride over a conductively-doped silicon material and a silicon oxide. For instance, it can be desired to deposit silicon nitride over conductively-doped polycrystalline silicon to form an insulative material over the polycrystalline silicon, and to simultaneously deposit the silicon nitride over borophosphosilicate glass (BPSG) to form a barrier layer over the BPSG.
A difficulty that can occur during such simultaneous deposition of silicon nitride is that the silicon nitride can form much more rapidly over the polycrystalline silicon than over the BPSG. Specifically, a nucleation rate of silicon nitride on silicon is typically significantly higher than it is on silicon oxides. Accordingly, the silicon nitride thickness over the polycrystalline silicon will be much thicker than that over the silicon oxide. For instance, a 50 Å thick silicon nitride layer can be formed on hemispherical grain polysilicon in about the time that it takes to grow a 20 Å thick silicon nitride layer on BPSG. The 20 Å thick silicon nitride layer may not be sufficient to be a suitable barrier layer to subsequent penetration of undesirable materials through the silicon nitride and into the BPSG. If materials penetrate into the BPSG, they can subsequently penetrate through the BPSG and to an underlying active region, which can ultimately cause failure of devices formed relative to the active region.
One solution to the above-described difficulty is to grow a thicker layer of silicon nitride on the polycrystalline silicon to enable a sufficiently thick barrier layer to be formed on the BPSG. However, such can result in too thick of a silicon nitride layer being deposited on the polycrystalline silicon for later use as a dielectric material in a capacitor device. It would be desirable to develop methodology whereby silicon nitride can be simultaneously deposited over a silicon oxide and a conductively-doped silicon material, with the deposition rate being substantially the same over both the silicon oxide-containing material and the conductively-doped silicon material.